The present invention relates to a light measuring device for measuring the intensity distribution of light, and more particularly to a light measuring device for use in a focus detecting apparatus for example for a camera.
In the focus detecting apparatus for a camera it is already known to form a light image of an object on a photoelectric sensor array and to detect the focusing of said object by the photoelectric output of said array representing the intensity distribution of said light image. The photoelectric output from said photoelectric sensor array, consisting of time-sequential pulses corresponding to the light intensities on the photoelectric sensors, often becomes unable to provide the difference information because of the saturation of the signal amplifier in case the object has a high average luminance giving rise to a high illumination intensity of the light image. On the other hand the information required for the focus detection is the distribution of the light intensity, i.e. the difference of the output signals from the photoelectric sensors. Consequently it is desirable, in the amplification of the time-sequential pulse output from the photoelectric sensor array, to amplify only the difference with respect to a reference voltage selected suitably according to the DC level of said output.